Cellulosic particles and methods of making them

ABSTRACT

Cationic cellulose particles useful in papermaking comprise from greater than 10 up to 50 percent by weight on cellulose of a polymeric amine of weight-average molecular weight in the range from 100,000 to 1,000,000 comprising monomeric units having the formula: 
     
       
         —XCR 3 ((CH 2 ) n NR 1 R 2 )(CH 2 ) m — 
       
     
     where X is selected from the group consisting of a chemical bond, O and NR 4 ; R 1  and R 2  are the same or different and are selected from the group consisting of H, C 1 -C 4  alkyl, phenyl and phenyl substituted with one, two or three substituents selected from the group consisting of C 1 -C 4  alkyl, C 1 -C 4  alkoxy, F, Cl and Br; R 3  and R 4  are independently selected from the group consisting of H, methyl and ethyl; m is an integer in the range from 1 to 4; and n is an integer in the range from 0 to 4.

FIELD OF THE INVENTION

This invention relates to cellulosic particles of the kind known asfibrids and to methods of making the same.

Cellulosic fibrids can be made by mixing together under turbulentconditions a spinning solution of cellulose and a coagulating liquor.One example of such a solution is viscose, which contains sodiumcellulose xanthate. Examples of coagulating liquors for viscose includeaqueous salt solutions and aqueous acid solutions. The fibrids soproduced comprise, often predominantly, fine fibrous particles a fewmicrons in diameter; of comparable size to the fibres in woodpulp. Thesefibrids may also comprise platelike or globular particles of similarsize to those fibres and of more or less irregular shape. For example,in the familiar salt figure test for viscose ripeness, viscose is mixedwith aqueous sodium chloride. If the sodium chloride concentration istoo low, a solution is formed; if it is too high, a more or lesscoherent precipitated lump is formed; but at the correct concentration,fibrids are formed. The fibrids formed in the salt figure test containresidual xanthate groups. If such fibrids are acidified, or if an acidiccoagulating liquor is used, then the xanthate groups are destroyed andcellulose is regenerated.

BACKGROUND ART

Modified cellulose particles have been proposed as additives inpapermaking, in particular to assist in formation of the paper web(sheet) and in sludge dewatering. In a series of papers in Das Papier(1980, vol. 34, pp. 575-579; 1981, vol. 35, pp. V33-V38 and pp. 555-562;and 1983, vol. 37, pp. 181-185), Kaufer et al. disclose cationicallymodified cellulose particles prepared by the reaction of woodpulp withreagents such as 3-chloro-2-hydroxypropyltrimethylammonium chloride andthe use of such particles as additives in papermaking.

Philipp and Lang (Faserforschung und Textiltechnik, 1966, vol. 17, pp.299-304) disclose the addition of poly(ethyleneimine) to diluted viscoseand titration of the resulting mixture with aqueous acid. A precipitateformed at mildly or moderately alkaline pH (8-11), depending upon theexact experimental conditions. The precipitate is described as a floc,indicating that it was composed of fibrids. The first formed precipitatewas believed to comprise a salt of a polymeric cation (protonatedpoly(ethyleneimine)) and a polymeric anion (cellulose xanthate). Theauthors refer to such salts generically as “symplexes”. Titration wascontinued until the mixture became acid (pH 3), and at least partialregeneration of cellulose xanthate to cellulose occurred, thus yieldingcationically modified cellulosic particles by a viscose process. Philippand co-workers elsewhere propose the use of cationically modifiedcellulose particles and symplexes as additives for use in papermaking(Dawydoff et al., Acta Polymerica, 1987, vol. 38, pp. 307-313, andPhilipp et al., Progress in Polymer Science, 1989, vol. 14, pp. 91-172).

WO-A-96/26220 discloses a process in which a cationic polyelectrolyte isadded to diluted viscose and the resulting mixture is mixed with acoagulating and regenerating liquor such as dilute sulphuric acid toform cationic cellulosic fibrids useful as additives in papermaking. Theviscose was added to the coagulating liquor, or vice versa. Suchpolyelectrolytes include polydialkyldiallylammonium salts, in particularpolydialkyldiallylammonium chloride (polyDADMAC), dicyandiamide,dicyandiamide condensates, polyamines, polyimines such aspoly(ethyleneimine), and ionenes. The viscose may contain about 30percent by weight of the polyelectrolyte on cellulose.

DISCLOSURE OF THE INVENTION

We have found that, when viscose containing a cationic polymer such as apolymeric amine is coagulated and regenerated in an acid bath, a highproportion of the cationic polymer may dissolve in the acid bath insteadof becoming incorporated (as is desired) in the precipitated andregenerated cellulose. Furthermore, some of the polymer may dissolve outof the regenerated cellulosic article during washing to removeimpurities or during subsequent use. This is a significant problem,particularly in the manufacture and use of regenerated cellulosicarticles which contain a high proportion of cationic polymer so as toexhibit high cationic activity and which have a high surface-to-volumeratio, for example cationic cellulosic fibrids.

According to the invention, there is provided a cationic cellulosicfibrid characterised in that it comprises from greater than 10 up to 50percent by weight on cellulose of a polymeric amine of weight-averagemolecular weight in the range from 100,000 to 1,000,000 comprisingmonomeric units having the formula:

—XCR³((CH₂)_(N)NR¹R²)(CH₂)_(m)—

where X is selected from the group consisting of a chemical bond, O andNR⁴; R¹ and R² are the same or different and are selected from the groupconsisting of H, C₁-C₄ alkyl, phenyl, and phenyl substituted with one,two or three substituents selected from the group consisting of C₁-C₄alkyl, C₁-C₄ alkoxy, F, Cl and Br; R³ and R⁴are independently selectedfrom the group consisting of H, methyl and ethyl; m is an integer in therange from 1 to 4; and n is an integer in the range from 0 to 4.

According to the invention, there is further provided a method for themanufacture of cationic cellulosic fibrids, including the steps of:

(a) combining viscose with an aqueous solution of a polymeric amine,thereby forming an amine-containing dope;

(b) mixing the amine-containing dope with a coagulating and regeneratingliquor under turbulent conditions, thereby forming a slurry of cationiccellulosic fibrids in a spent liquor; and

(c) collecting the cationic cellulosic fibrids from the spent liquor,

characterised in that the amine-containing dope contains from greaterthan 10 up to 50 percent by weight on cellulose of a polymeric amine ofweight-average molecular weight in the range from 100,000 to 1,000,000comprising monomeric units having the formula:

—XCR³((CH₂)_(n)NR¹R²)(CH₂)_(m)—

where X is selected from the group consisting of a chemical bond, O andNR⁴; R¹ and R² are the same or different and are selected from the groupconsisting of H, C₁-C₄ alkyl, phenyl, and phenyl substituted with one,two or three substituents selected from the group consisting of C₁-C₄alkyl, C₁-C₄ alkoxy, F, Cl and Br; R³ and R⁴ are independently selectedfrom the group consisting of H, methyl and ethyl; m is an integer in therange from 1 to 4; and n is an integer in the range from 0 to 4. Theexpression “spent liquor” is used as a convenient name for the byproductliquor produced in the method of the invention; it will be appreciatedthat this liquor often retains some coagulating and regenerating powers.

The weight-average molecular weight of the polymeric amine is preferablyin the range from 200,000 to 500,000. The polymeric amine is preferablya poly(vinylamine), for example a partially-hydrolysedpoly(N-vinylformamide) as disclosed by F Linhart and W.Auhorn (DasPapier, 1992, vol. 46(10A), pp. V38-V45). EP-A-0,692,599 discloses themanufacture of cellulosic fibres which contain polymeric amines, inparticular by the viscose process. The polymeric amines ofEP-A-0,692,599 comprise an aliphatic backbone with pendent amine groupsas specified for use in the present invention, and they are of molecularweight above 1000. The amount of polymeric amine disclosed inEP-A-0,692,599 may be in the range from 0.1 to 10, preferably from 0.3to 3, percent by weight on the cellulose in the spinning solution (e.g.viscose). The fibres of EP-A-0,692,599 exhibit improved dyeability andincreased wet and dry tenacities.

We have found that the method of the invention permits the incorporationof polymeric amine into cationic cellulosic fibrids with a high degreeof efficiency and that a high proportion of the polymeric amine remainswithin the fibrids of the invention during aqueous processing, forexample when used as additives in papermaking to assist in web formationor sludge dewatering. We have found that 80 percent or more, often 90percent or more, of the amine becomes incorporated into the fibrids. Incontrast, we have found that the efficiency of incorporation of othertypes of polymeric amine into cellulosic fibrids is rarely as high as 60percent. Surprisingly, we have been unable satisfactorily to spin fibresfrom viscose containing more than about 3 percent by weight on celluloseof the polymeric amine used in the invention: spinning stability wasextremely poor. In contrast, we have found no difficulty in spinningfibres from viscoses containing up to 25-30 or even 50-60 percent byweight on cellulose of polymeric amines outside the scope of the presentinvention such as aminated starch.

We have found it convenient to employ a conventional viscose suitablefor fibre manufacture and to employ an amine-containing dope containingfrom 1 to 8 percent by weight cellulose.

The coagulating and regenerating liquor may be any of those known forviscose processes, particularly aqueous acid. Conveniently, it is diluteaqueous sulphuric acid, which is the most usual acidic component in suchliquors, preferably at a concentration in the range from 0.5 to 5, morepreferably from 1 to 3.5, percent by weight. If desired, the liquor maycontain conventional amounts of sodium sulphate (a byproduct of theprocess), for example up to 25 percent by weight. This is advantageous,because the liquor can accordingly be recovered for reintroduction intothe process using conventional measures such as evaporation andcrystallisation. We have found that the liquor does not need to contain,and preferably contains little or no, auxiliary coagulating substancessuch as the zinc sulphate used in many processes for the manufacture ofconventional viscose fibres. Furthermore, the presence of suchsubstances in the fibrids produced by the method of the invention may beundesirable in some end-uses, for environmental and/or technicalreasons. IL desired, the liquor may contain conventional surface-activeagents as employed in other viscose processes.

The temperature of the coagulating and regenerating liquor is preferablyin the range from 60 to 100° C., more preferably in the range from 80 to95° C. Use of high temperatures makes for rapid coagulation andregeneration and assists removal of byproduct carbon disulphide andhydrogen sulphide by degassing. Degassing may be assisted by injectingsteam into the slurry resulting from mixing step (b). Suchsulphur-containing byproducts may be collected or disposed of inconventional manner.

The mixing step (b) is conveniently carried out by injecting both theamine-containing dope and the coagulating and regenerating liquor into ahigh-shear mixing chamber, for example a Y-shaped chamber, or mixinghead, although any method of mixing which generates sufficientturbulence and shear to produce the desired fibrids may be employed.

The method of the invention may be carried out batchwise orcontinuously. The collection step may be performed using conventionalmethods such as settling, filtration or centrifugation. The spent liquoris preferably. recovered by conventional methods such as evaporation andcrystallisation for reuse as coagulating and regenerating liquor.

Cationic activity of fibrids can be assessed by adding excess of anaqueous solution of an anionic water-soluble polymer followed byback-titrating with an aqueous solution of a cationic water-solublepolymer. The strength of the reagent solutions is conveniently about 1millinormal. The cationic activity of the fibrids of the invention maybe in the range from 500 to 5000, often 1000 to 5000, milliequivalentsper kg.

The fibrids of the invention may be used in the manufacture of paper andboard, including fine and speciality papers. The fibrids of theinvention are useful as additives in papermaking, particularly to assistwith web (sheet) formation and with sludge dewatering.

The invention is illustrated by the following Example, in which partsand proportions are by weight unless otherwise specified:

EXAMPLE

Viscose was mixed with water and aqueous solutions of various polymericamines to give diluted viscoses containing 2-4% cellulose and knownamounts of amine. These diluted viscoses were mixed with aqueoussulphuric acid (2.7%) under turbulent conditions to produce a slurrycontaining cationic cellulose fibrids (0.5-1%). In some experiments, thetemperature of the acid was 80° C., to assist degassing; in otherexperiments, mixing was carried out at ambient temperature and theresulting fibrid slurry heated to 80° C. to allow degassing to occur.Fibrids were collected from the slurry by filtration, washed andanalysed for nitrogen content by the Kjeldahl method. The efficiency ofincorporation of the polymeric amine into the fibrids was calculatedfrom the analytical and theoretical values for nitrogen content. Theresults shown in Table 1 were obtained:

TABLE 1 Amine on Nature of amine (supplier, Trade Mark) cellulose %Efficiency % Comparative experiments: Aliphatic polyamine derivative24.8 21.9-32.4 (Clariant UK, Cartafix DPRS) (3) Poly(ethyleneimine)(BASF, Polymin P) 25.0 61.4 Poly(ethyleneimine) (BASF, Polymin P) 37.953.9 Poly(ethyleneimine) (BASF, Polymin P) 50.8 54.9 Poly(DADMAC)(Allied Colloids, 14.0 31.3 Alcofix 169) Aminated starch (Südstärke,Licocat) 63.7 43.2-44.1 (2) Aminated starch (Südstärke, Licocat) 127.343.8 Experiments according to the invention: Poly(vinylamine) (BASF,Basocoll PR8086) 25.0 89.1 Poly(vinylamine) (BASF, Basocoll PR8086) 37.690.0 Poly(vinylamine) (BASF, Basocoll PR8086) 49.9 87.1 Poly(vinylamine)(BASF, Catiofast PR8106) 12.5 91.1-92.3 (2) Poly(vinylamine) (BASF,Catiofast PR8106) 13.4-13.8 96.1-99.1 (3) Poly(vinylamine) (BASF,Catiofast PR8106) 17.8-18.1 89.6-92.2 (2) Poly(vinylamine) (BASF,Catiofast PR8106) 37.4 87.8 Poly(vinylamine) (BASF, Catiofast PR8106)50.2 81.0

Replicate experiments are indicated where relevant by numbers inparenthesis. The nominal weight-average molecular weights of both thepoly(vinylamine)s was 300,000-400,000.

What is claimed is:
 1. A cationic cellulosic fibrid, which comprisesfrom greater than 10 up to 50 percent by weight on cellulose of apolymeric amine of weight-average molecular weight in the range from100,000 to 1,000,000 comprising monomeric units having the formula:—XCR³((CH2)₂NR¹R²)(CH2)_(m)— where X is selected from the groupconsisting of a chemical bond, O and NR⁴; R¹ and R2 are the same ordifferent and are selected from the group consisting of H, C₁-C₄ alkyl,phenyl, and phenyl substituted with one, two or three substituentsselected from the group consisting of C₁-C₄ alkyl, C₁-C₄ alkoxy, F, Cland Br; R³ and R⁴ are independently selected from the group consistingof H, methyl and ethyl; m is an integer in the range from 1 to 4; and nis an integer in the range from 0 to
 4. 2. A fibrid according to claim1, wherein the weight-average molecular weight of the polymeric amine isin the range from 200,000 to 500,000.
 3. A fibrid according to claim 1,wherein the polymeric amine is a poly(vinylamine).
 4. A fibrid accordingto claim 1, which has a cationic activity in the range from 500 to 5000milliequivalents per kg.